1. Field of the Invention
The invention relates to a filter comprising a filter housing with an essentially horizontal partition wall that divides the filter housing into a clean-air chamber and a dust chamber, said partition wall being provided with a number of openings in which a number of filter bags are arranged that are secured to the partition wall and extend down into the dust chamber; said filter being provided with an inlet portion in open communication with the dust chamber in a level that is above a lowermost end of the filter bags, wherein the inlet portion is configured for introducing a dust-containing flow of air to the dust chamber, from where it can be sucked up through the filter bags into the clean-air chamber, from where the filtered air is discharged through a clean-air outlet.
2. The Prior Art
Such filters are commonly known (see eg WO 01/03808). Each of the filter bags typically comprises a wire frame on which a bag of a filter material is mounted. These filter bags are suspended from a horizontal partition wall down into a dust chamber, whereto the dust containing air is supplied and sucked upwards above the partition wall through the filter bags. Thereby the dust particles are deposited on the filter bags and drop down to the bottom of the filter housing from where they can be removed.
The present invention relates to the type of filters where the dust containing air is supplied at a level that is level with the filter bags, ie at a level that is above the lowermost end of the filter bags. Filter types are known, where the air is supplied underneath the filter bags, but the present invention is not relevant in connection with these filter types.
When the dust-containing air is supplied to the dust chamber in level with the filter bags, a certain wear occurs on the filter bags, in particular those filter bags that are arranged most proximate the inlet. Usually this wear is limited by requirements being made that a comparatively long rectilinear pipe be used that is connected to a tangential inlet for the dust chamber, whereby the flow of air achieves an optimal velocity profile within the supply pipe before it is deflected and partially braked by the inlet that is usually shaped to be 90°-180° helical. However, in many cases the requirement to use a long, rectilinear supply pipe is overridden by space or cost considerations, which means that the dust-containing flow of air is very turbulent when it enters the helical inlet. This means that the flow of air is unable to follow the helical inlet in an optimal manner, and it will quickly spread into the dust chamber and immediately affect in particular those filter bags that are situated close to the inlet. In particular in that area the filter bags will therefore comparatively quickly be worn by the air's dust particles with an ensuing reduction of filtration rating and requirements to filter bag exchanges.
Moreover, erroneous piping before the filter may cause increased wear on the filter bags due to the dust particles in the air also causing the filter bags to vibrate with an ensuing risk of breakdown.
In order for a filter of this type to function optimally, it is thus necessary to make high demands to the tubing before the inlet of the filter, whereby the optimal velocity profile of the dust-containing flow of air can be ensured.
It is a further drawback of helical inlets that the inlet is to be dimensioned precisely in accordance with the plant in which the filter is to be used, both with regard to the cross sectional area of the inlet and with regard to whether it has to be a clockwise or a counter-clockwise inlet. This means that the filter will not necessarily function optimally if, at a later stage, it is to be used for filtering a flow of air containing another product, or if a larger or smaller amount of air is used than was originally intended. Likewise, there may be problems with the piping if the filter is to be moved to another process plant.
It is the object of the invention to provide a filter of the above-mentioned type whereby it is possible to obtain a considerably higher degree of freedom with regard to the piping before the filter inlet, without an increased wear on the filter bags occurring. Moreover, the filter must be able to be used in changed operating conditions without ensuing problems.